One example of conventional air batteries is described in Japanese Patent Unexamined Publication No. 58-32750. The air battery described in Japanese Patent Unexamined Publication No. 58-32750 includes a battery composed of a plurality of unit cells. Electrolytic solution is circulated from a storage tank during the charge, but the storage tank is separated off and the electrolytic solution is circulated from a drainage tank that is attached with the battery during the discharge. The air battery also includes a filter for the electrolytic solution between the storage tank and a pressure pump that supplies the battery with the electrolytic solution from the storage tank.